Excitonic effect in the optical spectrum of semiconductors

Castillo-Mussot, Marcelo del; Sham, L. J.

doi:10.1103/physrevb.31.2092

Cited by 46 publications

(11 citation statements)

References 22 publications

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“…The experimental peak positions labeled E, and E2 are at 7.03 and 7.63 eV. This suggests that strong continuum excitonic effects of the type discussed by del Castillo-Mussot and Sham [17] for Si and Ge may be associated with these critical points. The net effect of these excitonic phenomena is to shift oscillator strength to lower energies.…”

Section: Uv Optical Response Ganmentioning

confidence: 90%

“…Since a particularly large region of truly parallel bands occurs along A near X we speculate that its excitonic strength could be quite pronounced. In fact, del Castillo-Mussot and Sham [17] found that the E2 transition is reduced in intensity by these many-particle effects and gives rise to an exciton quasi bound state which for Si occurs 0.2 eV below the E2 edge. Because the high-frequency dielectric constant is considerably lower in GaN, we may expect an even larger excitonic shift.…”

Section: Uv Optical Response Ganmentioning

confidence: 96%

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Electronic and Optical Properties of the Group-III Nitrides, their Heterostructures and Alloys

et al. 1995

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Various aspects of the electronic structure of the group III nitrides are discussed. The relation between band structures and optical response in the vacuum ultraviolet is analyzed for zincblende and wurtzite GaN and for wurtzite AIN and compared with available experimental data obtained from reflectivity and spectroscopic ellipsometry. The spin-orbit and crystal field splittings of the valence band edges and their relations to exciton fine structure are discussed including substrate induced biaxial strain effects. The band-offsets between the III-nitrides and some relevant semiconductor substrates obtained within the dielectric midgap energy model are presented and strain effects which may alter these values are discussed. The importance of lattice mismatch in bandgap bowing is exemplified by comparing Al.Gali.N and InGal_,N. INTRODUCTIONThe interest in group-Ill nitrides for opto-electronic applications is currently experiencing an explosive growth. Still, many of their fundamental materials properties are only poorly known in comparison with other semiconductors. In this paper, we review the current state of understanding of their band structure and related optical properties and discuss some particular aspects in detail.While many band structure calculations have appeared over the last few years, (See [1] for an overview), the majority of these calculations have focused on obtaining a few of the important total energy properties such as lattice constants, bulk moduli and a general picture of the band structure without providing much discussion of their relation to experimental probes of the band structure. The early band structure work of the 1960's [2] used the semi-empirical pseudopotential method in which UV reflectivity data are used to adjust pseudopotential parameters. While by construction that approach accounts reasonably well for the optical response functions as they were known at the time, it suffers from non-uniqueness in assigning particular interband transitions to observed features in reflectivity. It turns out that the band structures obtained in this manner differ greatly from several recently reported band structure results based on the

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Section: Uv Optical Response Ganmentioning

confidence: 90%

Section: Uv Optical Response Ganmentioning

confidence: 96%

Electronic and Optical Properties of the Group-III Nitrides, their Heterostructures and Alloys

et al. 1995

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“…In both E 1 (including E 1 þ D 1 ) and E 2 transitions, all peaks shift to lower photon energy and the amplitude of the peak significantly reduces, whereas the peak becomes broader. For the E 1 , E 1 þ D 1 transitions, the sharp drop-off of the peak intensity has been intensively studied since the 1960s, for example, by del Castillo-Mussot et al 34 In that paper, the authors concluded that the electron-hole interaction, i.e., the excitonic effect, plays an important role in the behaviour of these transitions, particularly for E 1 and E 1 þ D 1 , where the effect increases the strength of these transitions. In other words, the decreasing amplitude of these transitions is due to a reduction in the excitonic effect in the structure.…”

Section: Discussionmentioning

confidence: 99%

“…This technique has been used since the 1970s to study the band structure of semiconductors, [30][31][32][33][34] and, with an extended range of photon energy, it is capable of characterising optical transitions beyond the band edge. Based on these optical transitions, the electronic band structure of Ge 1Àx Sn x was studied.…”

Section: Methodsmentioning

confidence: 99%

Synthesis of Ge1−xSnx alloys by ion implantation and pulsed laser melting: Towards a group IV direct bandgap material

Tran

Pastor

Gandhi

et al. 2016

Journal of Applied Physics

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The germanium-tin (Ge1−xSnx) material system is expected to be a direct bandgap group IV semiconductor at a Sn content of 6.5−11 at. %. Such Sn concentrations can be realized by non-equilibrium deposition techniques such as molecular beam epitaxy or chemical vapour deposition. In this report, the combination of ion implantation and pulsed laser melting is demonstrated to be an alternative promising method to produce a highly Sn concentrated alloy with a good crystal quality. The structural properties of the alloys such as soluble Sn concentration, strain distribution, and crystal quality have been characterized by Rutherford backscattering spectrometry, Raman spectroscopy, x ray diffraction, and transmission electron microscopy. It is shown that it is possible to produce a high quality alloy with up to 6.2 at. %Sn. The optical properties and electronic band structure have been studied by spectroscopic ellipsometry. The introduction of substitutional Sn into Ge is shown to either induce a splitting between light and heavy hole subbands or lower the conduction band at the Γ valley. Limitations and possible solutions to introducing higher Sn content into Ge that is sufficient for a direct bandgap transition are also discussed.

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“…However, the importance of the excitonic effects has been known for a long time, even in cases in which the features are less characteristic than, the appearance of a hydrogenic series of bound states in the band gap. Excitonic effects in the absorption line shape of semiconductors above the fundamental gap were calculated some time ago (Hanke and Sham, 1974del Castillo and Sham, 1985). Hanke and Sham (1980) solved the Bethe-Salpeter equation [Eq.…”

Section: The Effects Of the Electron-hole Interactionmentioning

confidence: 99%

Electronic excitations: density-functional versus many-body Green’s-function approaches

2002

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Electronic excitations lie at the origin of most of the commonly measured spectra. However, the first-principles computation of excited states requires a larger effort than ground-state calculations, which can be very efficiently carried out within density-functional theory. On the other hand, two theoretical and computational tools have come to prominence for the description of electronic excitations. One of them, many-body perturbation theory, is based on a set of Green's-function equations, starting with a one-electron propagator and considering the electron-hole Green's function for the response. Key ingredients are the electron's self-energy ⌺ and the electron-hole interaction. A good approximation for ⌺ is obtained with Hedin's GW approach, using density-functional theory as a zero-order solution. First-principles GW calculations for real systems have been successfully carried out since the 1980s. Similarly, the electron-hole interaction is well described by the Bethe-Salpeter equation, via a functional derivative of ⌺. An alternative approach to calculating electronic excitations is the time-dependent density-functional theory (TDDFT), which offers the important practical advantage of a dependence on density rather than on multivariable Green's functions. This approach leads to a screening equation similar to the Bethe-Salpeter one, but with a two-point, rather than a four-point, interaction kernel. At present, the simple adiabatic local-density approximation has given promising results for finite systems, but has significant deficiencies in the description of absorption spectra in solids, leading to wrong excitation energies, the absence of bound excitonic states, and appreciable distortions of the spectral line shapes. The search for improved TDDFT potentials and kernels is hence a subject of increasing interest. It can be addressed within the framework of many-body perturbation theory: in fact, both the Green's functions and the TDDFT approaches profit from mutual insight. This review compares the theoretical and practical aspects of the two approaches and their specific numerical implementations, and presents an overview of accomplishments and work in progress. CONTENTS

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Excitonic effect in the optical spectrum of semiconductors

Cited by 46 publications

References 22 publications

Electronic and Optical Properties of the Group-III Nitrides, their Heterostructures and Alloys

Electronic and Optical Properties of the Group-III Nitrides, their Heterostructures and Alloys

Synthesis of Ge1−xSnx alloys by ion implantation and pulsed laser melting: Towards a group IV direct bandgap material

Electronic excitations: density-functional versus many-body Green’s-function approaches

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